1. Field of the Invention
The present invention relates to a display device, and more particularly, to a liquid crystal display (LCD) device. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for stabilizing signals on a common voltage line in a pad region of the LCD device.
2. Discussion of the Related Art
In general, the liquid crystal display (LCD) device is a flat panel display device that has been actively researched due its advantages of high contrast ratio, desirable color display capacity and fast response time for displaying moving images. The LCD device has a lighter weight than a cathode ray tube (CRT) monitor and is also thinner than a cathode ray tube (CRT) monitor. Thus, an LCD device can be a display panel for use in a wall-mounted TV. In another example, an LCD device can be used as a display panel in a notebook computer powered by a battery due to its light weight, thin profile and low power consumption. Further, an LCD device can be manufactured to be a compact size, such as a miniature display panel for a mobile phone. The LCD device has a variety of applications due to its light weight, thin profile, low power consumption and scalability down to a compact size.
The LCD device includes an upper substrate, which is often referred to as a color filter layer array substrate, a lower substrate, which is often referred to as a TFT array substrate, and a layer of liquid crystal molecules disposed between the upper and lower substrates. Each of the upper and lower substrates can have an alignment film formed on an inner surface thereof. The alignment film has a pattern to orient the liquid crystal molecules in a predetermined direction. A related art liquid crystal display device will be described in detail with reference to FIG. 1 and FIG. 2.
FIG. 1 is a plan view of the related art liquid crystal display device, and FIG. 2 is a plan view illustrating a portion of a pad region of the related art liquid crystal display device shown in FIG. 1. An upper substrate (not shown) of the LCD device includes a black matrix (not shown) to prevent light leakage and a color filter layer (not shown) having red, green and blue color filters. As shown in FIG. 1, a lower substrate 11 is divided into an active region 11a (area inside the dotted line shown in FIG. 1) and a pad region 11b (area outside the dotted line shown in FIG. 1).
The active region 11a is a region on which an image is displayed. The active region 11a includes gate lines 12 crossing data lines 15 to define pixel regions. Common lines 17 also cross the data lines 15. Thin film transistors (not shown) are formed in each pixel region adjacent to where one of the gate lines 12 for the pixel region and one of the data lines 15 for the pixel region cross. In addition, pixel electrodes (not shown) are formed in each of the pixel regions and connected to the thin film transistors in each of the pixel region.
The pad region 11b includes gate pads 22 respectively connected to the gate lines 12, data pads 25 respectively connected to the data lines 15, and a common electrode 27 commonly connected to the common lines 17. The gate pads 22, the data pads 25 and the common electrode 27 receive signals from a printed circuit board (not shown) acting as a driving circuit.
As shown in FIG. 2, the lower substrate 11 has the gate lines 12 and the data lines 15 crossing each other to define pixels of red (R), green (G) and blue (B). Each of the pixels includes the thin film transistor acting as a switching element to apply a pixel voltage to the pixel electrode connected with the thin film transistor. The common lines 17 are parallel to the gate lines 12. Each gate pad 22 is integrally formed with a corresponding gate line 12 in a gate pad region G/P, and each data pad 25 is integrally formed with a corresponding data line 15 in a data pad region D/P. The common electrode 27 is connected to all of the common lines 17 in the gate pad region G/P. To prevent a short circuit with the gate lines, the common electrode 27 is in a different layer from the gate lines inside the gate pad region G/P, and is electrically connected with the common lines 17 via contact holes 30. The common lines 17 are in the same layer as the gate lines 12.
A data signal is applied to the data lines 15 via the data pads 25 and a Vcom signal for supplying a reference voltage for the data signal is applied to the common electrode 27. However, such a related art liquid crystal display device has interference problems between the data signal and the Vcom signal. The data signal Vdata is supplied as an AC signal. The common signal Vcom is supplied as a DC signal. Because the data lines having an AC signal overlap the common electrode, the AC signal in the data lines can cause a voltage ripple or distortion in the DC signal of the common lines. This voltage ripple or distortion of the Vcom-signal causes a ripple of the voltage gap between the pixel voltage and Vcom, and the ripple causes flickering of the images and/or greenish phenomena in the images.